Torque motor driving device for wire cut electrical discharge machines

ABSTRACT

In a torque motor driving device for wire cut electrical discharge machines, a voltage waveform rectified by a full-wave rectifying circuit, not using a high-capacitance electrolytic capacitor, is applied as an AC voltage to a single-phase torque motor by a bridge circuit including semiconductor switches. A PWM signal whose duty is adjusted so that the current flowing through the torque motor matches an instructed value is generated and the generated PWM signal is used for the operation of the bridge circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a torque motor driving device for wirecut electrical discharge machines that drives a torque motor with an ACpower source.

2. Description of the Related Art

A torque motor is best suited for feeding or winding the wire electrodeof a wire cut electrical discharge machine. In a wire cut electricaldischarge machine, an appropriate torque is generally applied to theshaft to which the wire electrode bobbin is attached, in the directionopposite to the wire electrode feed direction, to prevent the wireelectrode from being loosened. In known use of a torque motor in a wirecut electrical discharge machine described in, for example, JapanesePatent Application Publication No. 7-60552, a used wire electrode is notstored in a recovery box, and a wire electrode recovery bobbin driven bya torque motor is disposed on the wire electrode feed unit, so that thewire electrode can be recovered efficiently while the tension is keptconstant by controlling the torque motor.

The wire electrode is generally 0.02 mm (minimum wire electrodediameter) to 0.40 mm (maximum wire electrode diameter) in diameter. Athick wire electrode requires a large torque because the bobbin is largeand heavy and the inertia is large. A thin wire electrode requires asmall torque because the bobbin is small and light, the inertia issmall, and a torque large enough to break the wire electrode cannot beapplied. As described above, the output torque of a torque motor needsto be adjusted properly depending on the diameter of a wire electrode tobe used.

A torque motor is a type of induction motor and, when rotating so as tobe pulled in a direction opposite to that of a torque generating on theoutput shaft, the effective current flowing through the motor isapproximately proportional to the torque generating on the output shaft,regardless of the number of revolutions. Accordingly, to obtain adesired torque, the AC voltage to be applied to the motor needs to bechanged so that the current corresponding to the torque flows. Togenerate torques corresponding to the range from the maximum wireelectrode diameter to the minimum wire electrode diameter describedabove, the effective voltage needs to be changed to a value fromapproximately 5% to 100% of the rated voltage of the motor.

As a circuit that changes the AC voltage of a torque motor, a drivingcircuit adopting the resistor voltage divider method was usedconventionally. In recent years, however, a driving circuit adopting thetriac method has been used.

FIG. 6 schematically shows a torque motor driving circuit by theresistor voltage divider method. The resistor voltage divider methoddivides the power voltage V1 of an AC power source 10 using resistors51, 52, 53, 54, and 55 and a single-phase torque motor 20, and performsswitching using relays 61, 62, 63, 64, and 65, so that unnecessaryvoltages are applied to the resistors. In the resistor voltage dividermethod, it is necessary to prepare the resistors and relays required toapply a set voltage across the single-phase torque motor 20. Becausepower is consumed by the resistors, a plurality of large-size powerresistors are necessary, thereby increasing the device size. Inaddition, problems are that cost is high, a large loss of power iscaused, and the output torque of the single-phase torque motor 20changes depending on the power voltage V1 of an AC power source 10.

FIG. 7 schematically shows a torque motor driving circuit by the triacmethod. The triac method obtains a desired torque by changing the firingangle of a triac 68 to change the effective voltage to be applied to thesingle-phase torque motor 20. The triac method can reduce a loss ofpower and make a current to be applied to a torque motor coincide withan instructed value even in an area where a different power voltage isused by feeding back a detected current value to a firing angle controlcircuit (not shown). However, since control by this method is limited tothe commercial frequency of the AC power source 10, especially when alow torque is required, the firing angle becomes low and, as shown inFIG. 9, the ratio of the OFF time of the voltage to be applied to thesingle-phase torque motor 20 becomes much larger than that of the ONtime. As a result, fluctuations in a current flowing through thesingle-phase torque motor 20 become large as shown in FIG. 9B and thenumber of torque fluctuations for each turn increases.

To suppress torque fluctuations in the triac method, an inverter can beused to change the number of revolutions of the motor. An inverter isgenerally used to control the number of revolutions of an AC motor. ACpower is converted into DC power by a converter and a voltage to beapplied to the motor is converted into AC power again by a bridgecircuit including semiconductor switches. The so-called PWM control isallowed, in which the effective frequency of a motor is changed bydetermining the rotation frequency from several hertz to tens of hertzand the switching frequency of tens of kilohertz and changing the dutyat which the semiconductor switch is turned ON and OFF within theswitching frequency.

FIG. 8 schematically shows a torque motor driving circuit by theinverter method. The torque motor driving circuit by the inverter methodfull-wave rectifies the AC voltage of the AC power source 10 using adiode bridge converter including a first diode 11, a second diode 12, athird diode 13, and a fourth diode 14 and then smoothes and converts therectified voltage into a DC voltage using an inductor 70 and ahigh-capacitance electrolytic capacitor 72. The DC voltage is convertedinto an AC voltage again by an inverter including a first FET 15, asecond FET 16, a third FET 17, and a fourth FET 18, and the AC voltageis applied to the single-phase torque motor 20.

A PWM signal generating circuit 76 changes the ON/OFF duty of the PWMsignal to make the detected current value that a means (not shown)obtains by detecting the current flowing through the motor coincide withthe instructed current value, so that the current value matches theinstructed current value and the desired torque can be obtained evenwhen power fluctuations occur as shown in FIG. 10 or even in an area inwhich a different power voltage (such as 200 V or 220 V) is used. Inaddition, since the OFF time can be significantly reduced than in thetriac method, the current flowing through the coil of the single-phasethe torque motor 20 becomes continuous and torque fluctuations arereduced.

However, since the voltage to be applied to the single-phase torquemotor 20 is the DC voltage converted by the converter, if the switchingfrequency and the duty of the PWM signal are fixed, voltage fluctuationscaused when the polarity of the voltage is reversed become sharp,thereby causing torque fluctuations. Accordingly, a PWM/rotationfrequency signal synthesizing circuit 78 has a duty adjusting circuit79, which adjusts the duty of switching depending on the phase of therotation frequency so that the current waveform becomes sinusoidal asshown in FIG. 10 to prevent torque fluctuations. This duty adjustingcircuit 79 is a complicated circuit that gradually increases the duty sothat the phase of the rotation frequency has the minimum value at 0degrees and the maximum value at 90 degree and reduces the duty so thatthe phase has the minimum value at 180 degrees. On the other hand, anhigh-speed FET with a small ON resistance can be used as thesemiconductor switch to reduce a loss of power.

Since the resistor voltage divider method or triac method of the priorart has large torque fluctuations and other problems as described above,use of an inverter with less torque fluctuations can be considered.However, this method also has disadvantages. That is, the converter unitthat converts AC power into DC power generally uses the high-capacitanceelectrolytic capacitor 72 (see FIG. 8) to store the electrical energyrequired to supply the full-wave rectified DC voltage to the motor.

The electrolytic capacitor 72 greatly reduces its capacitance over timeand the reduction causes much heat generation due to charge anddischarge, possibly causing explosion or liquid leakage. Accordingly,the electrolytic capacitor 72 needs to have a large capacitance.However, a high-capacitance electrolytic capacitor is large andexpensive. To ensure long term reliability, it is necessary to give ahigher priority to long term reliability by increasing the capacitanceor give a higher priority to the size and const by reducing capacitancemargins.

For the single-phase torque motor 20, the rated power frequencies aregenerally 50 Hz and 60 Hz. The rotation frequency can be fixed to 50 Hzor 60 Hz, but a circuit that adjusts the duty of the switching dependingon the phase of the rotation frequency is required to obtain asinusoidal current waveform that prevents torque fluctuations and thiscircuit is complicated and expensive.

SUMMARY OF THE INVENTION

The present invention addresses the above problems with the object ofproviding a torque motor driving device for wire cut electricaldischarge machines that can output a low torque stably, has long termreliability and a low production cost, and drives a torque motor with anAC power source.

A torque motor driving device for wire cut electrical discharge machinesaccording to the present invention includes a full-wave rectifyingcircuit connected to the AC power source, a bridge circuit connectedbetween a rectification output of the full-wave rectifying circuit andthe torque motor, a polarity determination signal generating circuitthat detects a period during which an absolute value of a power voltageof the AC power source exceeds a first reference voltage in a periodduring which a polarity of the power voltage of the AC power source ispositive and outputs a detection result as a first polaritydetermination signal and detects a period during which the absolutevalue of the power voltage of the AC power source exceeds a secondreference voltage in a period during which the polarity of the powervoltage of the AC power source is negative, a PWM signal generatingcircuit that generates a PWM signal whose duty is adjusted according toa physical quantity corresponding to a torque of the torque motor, and alogical AND circuit that obtains a logical AND between the PWM signaloutput from the PWM signal generating circuit and the first and secondpolarity determination signals output from the polarity determinationsignal generating circuit. The bridge circuit includes a positivepolarity switch group having two or more semiconductor switches thatapplies a positive voltage to the torque motor and a negative polarityswitch group having two or more semiconductor switches that applies anegative voltage to the torque motor. In addition, at least one of thesemiconductor switches included in the positive polarity switch groupoperates according to a signal of a logical AND between the first orsecond polarity determination signal and the PWM signal and the othersemiconductor switches operate according the first or second polaritydetermination signal. At least one of the semiconductor switchesincluded in the negative polarity switch group operates according to asignal of a logical AND between the second or first polaritydetermination signal and the PWM signal and the other semiconductorswitches operate according the second or first polarity determinationsignal.

The physical quantity corresponding to the torque of the torque motorcan be any one of (1) an effective value of a current waveform of acurrent that flows into the torque motor or an average value obtained byfull-wave rectifying the current waveform, (2) an effective value of avoltage waveform of a voltage applied to the torque motor or an averagevalue obtained by full-wave rectifying the voltage waveform, (3) a shafttorque of an output shaft of the torque motor, and (4) a tension of awire electrode. The duty of the PWM signal may be changed so that thephysical quantity matches an instructed value that is input to a drivingcircuit for the torque motor.

An instructed value data table for the torque motor may be provided foreach wire electrode diameter and data corresponding to set wireelectrode diameter information may be retrieved from the instructedvalue data table and the data is input to the torque motor drivingcircuit as an instructed value.

When set power frequency information does not match a frequency in theinstructed value data table for the torque motor, a value in theinstructed value data table may be multiplied by a coefficient that hasa predetermined initial value and that is changeable later, and amultiplication result may be input to the torque motor driving circuitas an instructed value.

The instructed value data table for the torque motor for each wirediameter may be provided for each of a first frequency and a secondfrequency that is different from the first frequency, and the data tablefor the first frequency or the data table for the second frequency maybe selected depending on the set power frequency information.

According to the present invention, it is possible to provide a torquemotor driving device that can output a low torque stably and has longterm reliability and a low production cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematically shows an embodiment of a single-phase torquemotor driving circuit according to the present invention, which controlsthe detected current value obtained by detecting a current flowingthrough a single-phase torque motor so as to match an instructed currentvalue.

FIG. 2 shows an example of the voltage waveform of an AC voltagesupplied from the AC power source in FIG. 1.

FIGS. 3A and 3B show an example of the waveform of a voltage applied tothe signal-phase torque motor in FIG. 1 and an example of the waveformof a current flowing through the signal-phase torque motor.

FIG. 4A shows an example of the voltage waveform of the AC voltagesupplied from the AC power source in FIG. 1; FIG. 4B shows an example ofa rectified waveform obtained by full-wave rectifying the AC voltagewith a diode bridge circuit in FIG. 1; FIG. 4C shows an example of afirst polarity determination signal to be output in the period in whichthe polarity of the AC voltage is detected as positive; FIG. 4D shows anexample of a second polarity determination signal to be output in theperiod in which the polarity of the AC voltage is detected as negative;FIG. 4E shows an example of a PWM signal generated by a PWM signalgenerating circuit in FIG. 1; FIG. 4F shows an example of a signalresulting from a logical AND between the first polarity determinationsignal in FIG. 4C and the PWM signal in FIG. 4E; FIG. 4G shows anexample of a signal resulting from a logical AND between the secondpolarity determination signal in FIG. 4D and the PWM signal in FIG. 4E.

FIG. 5 shows that the first polarity determination signal in FIG. 4C andthe second polarity determination signal in FIG. 4D are both placed inthe low state in the period in which the power voltage of the AC powersource in FIG. 1 is between a first reference voltage and a secondreference voltage to provide a dead time.

FIG. 6 schematically shows a torque motor driving circuit by theresistor voltage divider method of the prior art.

FIG. 7 schematically shows a torque motor driving circuit by the triacmethod of the prior art.

FIG. 8 schematically shows a torque motor driving circuit by theinverter method of the prior art.

FIG. 9A shows an example of the voltage waveform and FIG. 9B shows anexample of the current waveform of a torque motor by the triac method.

FIG. 10A shows an example of the voltage waveform and FIG. 10B shows anexample of the current waveform of a torque motor by the invertermethod.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A torque motor driving circuit according to the present inventionapplies a voltage waveform rectified by a full-wave rectifying circuitto a torque motor as an AC voltage using a bridge circuit including asemiconductor switch, instead of using a high-capacitance electrolyticcapacitor. This facilitates application of a sinusoidal voltage waveformsimilar to the power voltage waveform to a single-phase torque motorwithout using a complicated circuit that adjusts the duty of switchingdepending on the phase of the rotation frequency used in an inverter.The voltage to be applied to the single-phase torque motor can beadjusted even in an area where a different power voltage to obtain adesired torque as in the inverter by generating a PWM signal whose dutyis adjusted so that the current flowing through the single-phase torquemotor matches the instructed value and using the generated PWM signal tooperate the bridge circuit.

An embodiment of the invention will be described below with reference tothe drawings. Elements identical or similar to those of the prior artare indicated by identical reference numerals.

FIG. 1 is shows an embodiment of a single-phase torque motor drivingcircuit according to the present invention, which controls the detectedcurrent value obtained by detecting the current flowing through asingle-phase torque motor 20 so as to match an instructed current value.

An AC power source 10 in FIG. 1 supplies an AC voltage V1 with the powervoltage waveform shown in FIG. 2. The power voltage waveform in FIG. 2is the same as that in FIG. 4A described later.

A main controller 42 has a function of totally controlling a wire cutelectrical discharge machine and has the same configuration (not shown)as in a known control unit for wire cut electrical discharge machines,which has an central processing unit (CPU), an input/output means, arecording means, a display means, etc. A first diode 11, a second diode12, a third diode 13, and a fourth diode 14 constitute a diode bridgecircuit. The power voltage V1 of the AC voltage supplied from the ACpower source 10 is full-wave rectified by the diode bridge circuit. Thefull-wave rectified waveform is shown in FIG. 4B.

A voltage with the full-wave rectified waveform in FIG. 4B is applied tothe single-phase torque motor 20 via a semiconductor bridge circuitincluding a first FET 15, a second FET 16, a third FET 17 and a fourthFET 18.

The first FET 15 and the fourth FET 18 constitute a positive polarityswitch group, which applies a positive voltage to the single-phasetorque motor 20. The second FET 16 and the third FET 17 constitute anegative polarity switch group, which applies a negative voltage to thesingle-phase torque motor 20. Here, an FET is an acronym for fieldeffect transistor.

A resistor 22 is inserted in series with the single-phase torque motor20, the voltage applied to the resistor 22 is full-wave rectified by afull-wave rectifying circuit 30 and smoothed by a smoothing circuit 32,and the DC voltage (detected voltage value) obtained by the smoothing isdetected. The waveform of the current flowing through the resistor 22 issimilar to that in FIG. 3B and the waveform of the voltage across theresistor 22 is also similar to that in FIG. 3B.

Since the resistance of the resistor 22 is known, the circuit constantof an amplification circuit 34 is set so that the current (detectedcurrent value) flowing through the single-phase torque motor 20 can be adetected from the detected voltage value. This detected current value isinput to a PWM signal generating circuit 38 as the average current valueof the single-phase torque motor 20. The PWM signal generating circuit38 generates a PWM signal e whose ON/OFF duty is changed so that thedetected current value matches the instructed current value (see FIG.4E).

A polarity determination signal generating circuit 36 compares the powervoltage V1 (see FIG. 4A) of the AC power source 10 with a firstreference voltage, detects the period of the positive polarity, andgenerates a first polarity determination signal c (see FIG. 4C).Similarly, the polarity determination signal generating circuit 36compares the power voltage V1 with a second reference voltage, detectsthe period of the negative polarity, and generates a second polaritydetermination signal d (see FIG. 4D). The polarity determination signalgenerating circuit 36 can use, for example, a comparator IC (not shown)to perform these comparison operations. The first polarity determinationsignal c may indicate the negative polarity period and the secondpolarity determination signal d may indicate the positive polarityperiod.

Since the first polarity determination signal c and the second polaritydetermination signal d are both placed in the low state in the period inwhich the power voltage V1 of the AC power source 10 is between thefirst reference voltage and the second reference voltage, a dead timecan be provided (see FIG. 5). This prevents the rectification voltagefrom being short-circuited by concurrent operation of the positivepolarity switch group and the negative polarity switch group.

The first polarity determination signal c output from the polaritydetermination signal generating circuit 36 is input to the first FET 15included in the positive polarity switch group and a logical AND circuit40. Similarly, the second polarity determination signal d output fromthe polarity determination signal generating circuit 36 is input to thethird FET 17 included in the negative polarity switch group and thelogical AND circuit 40. The logical AND circuit 40 calculates thelogical AND between the first polarity determination signal c and thePWM signal e and the logical AND between the second polaritydetermination signal d and the PWM signal e.

The fourth FET 18 in the positive polarity switch group is operated onthe basis of the logical AND (see FIG. 4F) between the first polaritydetermination signal c and the PWM signal e resulting from the logicalAND circuit 40. The first FET 15 in the positive polarity switch groupis operated by the first polarity determination signal c. The second FET16 in the negative polarity switch group is operated on the basis of thelogical AND (see FIG. 4G) between the second polarity determinationsignal d and the PWM signal e resulting from the logical AND circuit 40.The third FET 17 in the negative polarity switch group is operated bythe second polarity determination signal d. Accordingly, the voltageshown FIG. 3A is applied to the single-phase torque motor 20 and thecurrent shown in FIG. 3B flows through the single-phase torque motor 20.The current flowing through the single-phase torque motor 20 is obtainedby detecting the voltage across the resistor 22.

The fourth FET 18 may be replaced with the first FET 15, and the thirdFET 17 may be replaced with the second FET 16. The third FET 17 of thenegative polarity switch group instead of the positive polarity switchgroup may be operated on the basis of the logical AND between the firstpolarity determination signal c and the PWM signal e, and the second FET16 may be operated by the first polarity determination signal. Thefourth FET 18 of the positive polarity switch group instead of thenegative polarity switch group may be operated on the basis of thelogical AND between the second polarity determination signal d and thePWM signal e, and the first FET 15 may be operated by the secondpolarity determination signal. Alternatively, all the FETs in thepositive and negative polarity switch groups may be operated only by thelogical AND between the first and second polarity determination signalsc and d and the PWM signal e. When each of the first FET 15, the secondFET 16, the third FET 17, and the fourth FET 18 includes a plurality ofFETs connected in parallel because, for example, the rated currents ofthe FETs 15 to 18 are small, the plurality of FETs connected in parallelmay be operated by the same signal.

According to the embodiment of the present invention, it is possible toprovide a torque motor driving circuit that can easily apply asinusoidal switched voltage to a torque motor without using ahigh-capacitance smoothing capacitor or a circuit adjusting the duty ofswitching depending on the phase of the rotation frequency used in theinverter, that can output even a low torque stably, and that has longterm reliability and a low production cost.

In addition, a circuit that detects the current of the single-phasetorque motor 20 and adjusts the duty of the PWM signal e is disposed, sothat a desirable torque that depends on the diameter of a wire electrodecan be obtained even in an area in which the power voltage V1 isdifferent. As in the inverter, an high-speed FET or other component witha small resistance is used as the semiconductor switch, so that a lossof power can be reduced to a small value.

In the above embodiment of the present invention, the resistor 22 isinserted in series with the single-phase torque motor 20, the resistanceacross the resistor 22 is measured, the effective value of the currentwaveform applied to the single-phase torque motor 20 and the averagevalue obtained by full-wave rectifying the current waveform areobtained, and these values are used as physical quantities fordetermining the duty of the PWM signal e.

Other than this, there are a method that measures the output voltage ofthe torque motor driving circuit, a method that measures the shafttorque of the shaft to which the single-phase torque motor 20 is fixed,and a method that measures the tension of the wire electrode. The shafttorque can be estimated from the amount of strain obtained by placing atorque detector between the single-phase torque motor 20 and the fixedshaft or attaching a strain gauge to the output shaft of thesingle-phase torque motor 20. The tension of the wire electrode can beestimated by placing a tension detector in the running path of the wireelectrode drawn from the wire bobbin or estimated from the load currentof the motor that pulls the wire electrode.

The control unit for wire cut electrical discharge machines has aninstructed value data table for the single-phase torque motor 20 foreach wire electrode diameter, retrieves the data corresponding to setwire electrode diameter information from the instructed value datatable, and inputs the data to the driving circuit of the torque motor asan instructed value.

The instructed value table for the single-phase torque motor 20 is for50 Hz or 60 Hz. If the different power frequency information is set, thevalue in the instructed value data table is multiplied by a coefficientthat has a predetermined initial value and can be changed later and theresulting value is input to the torque motor driving circuit as aninstructed value.

The instructed value data table for the torque motor 20 for each wirediameter may be provided for each of 50 Hz and 60 Hz, and the instructedvalue data table for 50 Hz or the instructed value data table for 60 Hzmay be selected depending on the set power frequency information.

The above data tables can be stored in a recording means (not shown)included in the main controller 42.

1. A toque motor driving device for wire cut electrical dischargemachines that drives a torque motor using an AC power source, the toquemotor driving device comprising: a bridge circuit connected between arectification output of the full-wave rectifying circuit and the torquemotor; a polarity determination signal generating circuit that detects aperiod during which an absolute value of a power voltage of the AC powersource exceeds a first reference voltage in a period during which apolarity of the power voltage of the AC power source is positive andoutputs a detection result as a first polarity determination signal anddetects a period during which the absolute value of the power voltage ofthe AC power source exceeds a second reference voltage in a periodduring which the polarity of the power voltage of the AC power source isnegative; a PWM signal generating circuit that generates a PWM signalwhose duty is adjusted according to a physical quantity corresponding toa torque of the torque motor; and a logical AND circuit that obtains alogical AND between the PWM signal output from the PWM signal generatingcircuit and the first and second polarity determination signals outputfrom the polarity determination signal generating circuit; wherein thebridge circuit includes a positive polarity switch group including twoor more semiconductor switches that applies a positive voltage to thetorque motor and a negative polarity switch group including two or moresemiconductor switches that applies a negative voltage to the torquemotor; wherein at least one of the semiconductor switches included inthe positive polarity switch group operates according to a signal of alogical AND between the first or second polarity determination signaland the PWM signal and the other semiconductor switches operateaccording the first or second polarity determination signal; wherein atleast one of the semiconductor switches included in the negativepolarity switch group operates according to a signal of a logical ANDbetween the second or first polarity determination signal and the PWMsignal and the other semiconductor switches operate according the secondor first polarity determination signal.
 2. The toque motor drivingdevice for wire cut electrical discharge machines according to claim 1,wherein the physical quantity corresponding to the torque of the torquemotor is any one of (1) an effective value of a current waveform of acurrent that flows into the torque motor or an average value obtained byfull-wave rectifying the current waveform, (2) an effective value of avoltage waveform of a voltage applied to the torque motor or an averagevalue obtained by full-wave rectifying the voltage waveform, (3) anshaft torque of an output shaft of the torque motor, and (4) a tensionof a wire electrode, and the duty of the PWM signal is changed so thatthe physical quantity matches an instructed value input to a torquemotor driving circuit.
 3. The toque motor driving device for wire cutelectrical discharge machines according to claim 2, wherein aninstructed value data table for the torque motor is provided for eachwire electrode diameter and data corresponding to set wire electrodediameter information is retrieved from the instructed value data tableand the data is input to the torque motor driving circuit as aninstructed value.
 4. The toque motor driving device for wire cutelectrical discharge machines according to claim 3, wherein, when setpower frequency information does not match a frequency in the instructedvalue data table for the torque motor, a value in the instructed valuedata table is multiplied by a coefficient that has a predeterminedinitial value and that is changeable later, and a multiplication resultis input to the torque motor driving circuit as an instructed value. 5.The toque motor driving device for wire cut electrical dischargemachines according to claim 3, wherein the instructed value data tablefor the torque motor for each wire diameter is provided for each of afirst frequency and a second frequency that is different from the firstfrequency, and the data table for the first frequency or the data tablefor the second frequency is selected depending on the set powerfrequency information.